WO2011012238A1 - Oxyde de tungstène modifié et son procédé de préparation - Google Patents

Oxyde de tungstène modifié et son procédé de préparation Download PDF

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WO2011012238A1
WO2011012238A1 PCT/EP2010/004404 EP2010004404W WO2011012238A1 WO 2011012238 A1 WO2011012238 A1 WO 2011012238A1 EP 2010004404 W EP2010004404 W EP 2010004404W WO 2011012238 A1 WO2011012238 A1 WO 2011012238A1
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weight
process according
electrolytic solution
photoanode
anodization
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PCT/EP2010/004404
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English (en)
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Laura Meda
Alessandra Tacca
Carlo Alberto Bignozzi
Stefano Caramori
Vito Cristino
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Eni S.P.A.
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Priority to EP10732886A priority Critical patent/EP2459487A1/fr
Priority to CN201080042159XA priority patent/CN102548902A/zh
Priority to US13/388,139 priority patent/US20120186982A1/en
Publication of WO2011012238A1 publication Critical patent/WO2011012238A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G41/00—Compounds of tungsten
    • C01G41/02—Oxides; Hydroxides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G41/00—Compounds of tungsten
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G9/00—Electrolytic capacitors, rectifiers, detectors, switching devices, light-sensitive or temperature-sensitive devices; Processes of their manufacture
    • H01G9/20—Light-sensitive devices
    • H01G9/2027—Light-sensitive devices comprising an oxide semiconductor electrode
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C01P2002/52—Solid solutions containing elements as dopants
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/542—Dye sensitized solar cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a modified tungsten oxide and a process for its preparation.
  • tungsten oxide In the field of materials which can be used for the preparation of photoanodes, tungsten oxide (WO 3 ) is receiving increasing attention due to its promising photo-activity and numerous applications of the photoanodes produced with this material .
  • the effectiveness of a photoanode in the conversion of light radiations in an electric current depends on various factors, among which the extension of the surface area of the photoanode exposed to the radiations and the extension of the spectral range of the absorbed photons which can be converted into electric current.
  • electrolytic solution in which the anodization process is carried out is generally a mixture of one or more inorganic acids in water (for example sulfuric, oxalic, hydrofluoric acid) .
  • inorganic acids for example sulfuric, oxalic, hydrofluoric acid
  • electrolytic solutions in which, instead of water, organic solvents are used as main solvent, such as ethylene glycol, or mixtures of these with water.
  • photoanodes of WO 3 by anodization of metal tungsten carried out under the above electrolytic solutions, allows photoelectrodes of metal tungsten to be obtained, having a surface consisting of WO 3 nanostructures with dimensions varying from 10 to 100 nm (nanostructured WO 3 ) .
  • This morphology gives the photoanodes a high specific surface of oxide which can be exposed to light radiation.
  • Photoanodes having WO 3 nanostructured surfaces known in the state of the art have a rather limited conversion capacity of photons into photocurrents, as they are only capable of effectively converting photons having a frequency falling within the region of the ultraviolet spectrum (wavelength ranging from 10 to 380 nm) .
  • the doping techniques used in the state of the art are not capable of introducing doping elements inside the crystalline lattice of the oxide in a sufficient quantity for significantly improving its conversion capacity of the photons into photocurrents and, consequently, the photoelectrochemical activity.
  • An objective of the present invention is to overcome the drawbacks observed in the state of the art.
  • an objective of the present invention is to identify a modified tungsten oxide and a process for preparing this modified tungsten oxide, which can be used as photoanode, having an improved photoelectrochemical activity.
  • a first object of the present invention relates to a modified tungsten oxide having an atomic concentration of 0.5 to 7.0%, preferably from 2.0 to 5.0%, of nitrogen atoms in lattice position, with respect to the total number of atoms of the oxide, having a surface morphology, detectable by means of a scanning electron microscope, characterized by nanostructures in the form of vermiform or branched open swellings, preferably having a length ranging from 200 to 2,000 nm, and a width ranging from 50 to 300 nm, having an appearance similar to Rice Krispies.
  • a second object of the present invention relates to a process for preparing a modified tungsten oxide, comprising an anodization reaction (anodic oxidation) of metal tungsten, characterized in that the anodization is carried out with an electrolytic solution comprising:
  • a further object of the present invention relates to a photoanode of modified tungsten oxide according to the present invention.
  • modified tungsten oxide WO 3
  • WO 3 modified tungsten oxide containing from 0.5 to 7.0% of N atoms in lattice position, with an appearance similar to rice krispies, by the anodization of metal tungsten, preferably in the form of a lamina, in a suitable electrolytic solution.
  • the modified tungsten oxide according to the present invention when used as photoanode, is capable of producing higher photocurrent density with respect to those of the WO 3 photoanodes known in the state of the art.
  • the best photoelectrochemical activity is considered as being due to the particular surface morphology of the WO 3 obtained with the process object of the present invention, combined with the presence of nitrogen atoms (doping element) inserted in the crystalline lattice of the WO 3 (lattice position), i.e. inserted in the structure of the oxide in a position of the lattice normally occupied by an oxygen atom.
  • modified WO 3 to effectively convert to electric current, photons having wavelengths falling within the spectral range which, in addition to UV, also comprises a part of the visible region (up to about 470 nm) .
  • FIG. 1 schematic representation of a photoelectrolytic cell for testing the photoelectrochemical activity of WO 3 photoanode, object of the present invention
  • FIG. 6 image taken under a SEM scanning electron microscope (magnification: 10,00Ox) of a sample of tungsten oxide according to the present invention
  • an electro-chemical cell for example, in which the operating electrode 2 and the counter-electrode 3 are two laminas of metal W situated inside a suitable electrolytic solution 4 at a preferred distance from each other of 1 to 15 mm, more preferably from 2 to 10 mm.
  • the thickness of the tungsten laminas is not particularly important, but it preferably ranges from 0.5 to 5 mm.
  • the lamina which forms the cathode can also consist of metals different from W, provided they cannot be attacked by the electrolytic solution, for example Pt, Ni, steel or graphite.
  • the electrolytic solution in addition to the components previously specified, can optionally contain up to 50% by weight, preferably from 0 to 25% by weight, of a further organic solvent, for example an alcohol having from 1 to 5 carbon atoms, an organic acid having from 1 to 5 carbon atoms, a polar aprotic organic compound having from 1 to 4 carbon atoms and at least one atom selected from oxygen or halogen, particularly O or F.
  • Organic solvents of the above type are for example ethanol, propanol, acetic acid, ethylene glycol, tetrahydrofuran, acetone, ethyl acetate, diglyme, 3 , 3 , 3-trifluoropropanol .
  • the anodization process is preferably carried out maintaining the potential difference applied to the electrodes (potentiostatic anodization) constant.
  • the potential difference applied to the electrodes ranges from 5 to 60 V, preferably from 30 to 40 V.
  • the anodization process is prolonged for a time ranging from 1 to 72 hours, preferably from 5 to 72 hours, more preferably from 12 to 72 hours, even more preferably from 48 to 72 hours. It has been observed that prolonging the duration of the anodization for over 72 hours does not produce improvements in the performances of the photoanodes of modified WO 3 .
  • the surface of the tungsten lamina is converted to nanostructured tungsten oxide
  • the growth of the nanostructured WO 3 derives from the combination of two processes which take place during the anodization: the electrochemical formation of WO 3 , by reaction of metal tungsten with the oxygen of the species present in the electrolytic solution (in particular the oxygen of water) and the dissolution of part of the WO 3 formed as a result of the fluoride ions present in the electrolytic solution.
  • the dissolution of the oxide is assisted by the intense electric field which is established at the electrode- electrolytic solution interface by potential differences higher than 10 V.
  • an electrolytic solution comprising:
  • the electrolytic solution can optionally also contain a suitable organic solvent and other possible electrolytic salts, in order to improve the conductivity, as is known to experts in the field.
  • Nitrogenated organic compounds (i) which are particularly suitable for the present invention are compounds comprising from 1 to 25, preferably from 1 to 10, more preferably from 1 to 5, carbon atoms, and at least one nitrogen atom. These compounds (i) are advantageously liquid at the electrolytic process temperature, they are more advantageously liquid at room temperature .
  • Compounds of the above type are in particular organic amines and amides.
  • said nitrogenated organic compounds (i) are at least partially miscible with water, i.e. they advantageously form homogeneous mixtures of water/compound (i) comprising from 3 to 50% by weight, preferably from 10 to 50% by weight, of water.
  • the best results are obtained using as nitrogenated organic compound an organic amide having general formula (I)
  • - Ri is H, or a Ci-C 6 , preferably Ci-C 3 , alkyl group, or an amine group -NR 2 R 3 ;
  • R 2 and R 3 independently of each other, are H or a Ci-C 6 , preferably C x -C 3 alkyl group;
  • - A is a divalent group selected from CO, SO 2 , POR' , wherein R' independently has the same meaning as
  • NMF N-methyl-formamide
  • DMF N-dimethyl-formamide
  • methylsulfonamide N-methylmethylsulfonamide
  • hexamethyl phosphoramide urea (especially in a hydro- alcohol solution)
  • urea especially in a hydro- alcohol solution
  • the electrolytic solution preferably contains, as nitrogenated organic compound, an amide having the above general formula (I) wherein A is CO, R 2 or R 3 are independently H or Ci-C 3 and Ri has the meaning previously defined. Even more preferably, R 2 is H and R 3 is a Ci-C 3 alkyl.
  • the electrolytic solution comprises, as nitrogenated organic compound, a solvent selected from the group consisting of N-methyl- formamide (NMF) , N-ethylformamide, N-methylacetamide, N ethylacetamide, N, N-dimethyl-formamide (DMF).
  • NMF N-methyl- formamide
  • N-ethylformamide N-methylacetamide
  • N ethylacetamide N, N-dimethyl-formamide
  • DMF N-dimethyl-formamide
  • a second component of the electrolytic solution is the oxidizing compound of metal tungsten under electrolytic conditions, which can consist of any oxygen donor compound under these conditions, such as, for example, a peroxide in a concentration of 1 to 10% by weight or, preferably, water.
  • the water is present in the electrolytic solution in a concentration varying from 1 to 50% by weight with respect to the total weight of the electrolytic solution. More preferably, the concentration of the water is within the range of 5-30% by weight of the electrolytic solution, even more preferably within the range of 10-20% by weight.
  • oxidizing agent for example, hydrogen peroxide
  • this is preferably present in concentrations of 1 to 10% by weight.
  • the electrolytic solution also comprises fluoride ions.
  • fluoride ions can be added to the electrolytic solution, for example, in the form of hydrofluoric acid (HF) or fluoride salts, such as for example ammonium fluoride
  • alkylammonium fluorides such as tetraethylammonium fluoride and tetrabutylammonium fluoride
  • sodium fluoride NaF
  • the fluoride salts can be optionally present in combination with HF.
  • the level of acidity or basicity of the electrolytic solution is not particularly important for the purposes of the present invention. For practical reasons, however, relating to the solubility of the salts or electrolytes present in solution, it is convenient to operate under acid conditions, with a molar concentration of hydrogen ions ranging from 10 "6 to 1.
  • the lamina is extracted from the electrolytic solution and subjected to washing with deionized water and subsequently acetone.
  • the lamina is then preferably treated in an ultrasound bath in distilled water for five minutes. This treatment allows the removal of possible material weakly bound to the surface.
  • the lamina is subjected to heat treatment in air (calcination) according to the usual technique, normally at a temperature ranging from 450 to 600 0 C, preferably from 500 to 580 0 C, for a time ranging from 1 to 5 hours, preferably from 2 to 4 hours .
  • the calcination treatment has the purpose of improving the crystallinity degree of the WO 3 oxide obtained, reducing the defects of its crystalline lattice and increasing carrier conductivity.
  • the process, object of the present invention allows WO 3 modified (doped) with nitrogen atoms, to be obtained.
  • the nitrogen atoms are in fact inserted in the crystalline lattice of the WO 3 .
  • the doping of the WO 3 involves the substitution of oxygen atoms of the oxide with a quantity of nitrogen atoms which is such as to produce a concentration of bound N ranging from 0.5 to 7%, preferably from 2 to 5%, with respect to the total number of atoms of the modified (doped) oxide, as can be deduced from the shift towards low energies of the UV-Visible absorption band.
  • 0.1 more preferably ranging from 0.1 to 0.3.
  • XPS analyses show that the WO 3 photoanodes can have varying quantities of carbon atoms on the surface (up to 30% of the overall number of atoms present, preferably from 0 to 20%) .
  • the carbon atoms unlike the doping nitrogen atoms, do not belong to the crystalline lattice of WO 3 .
  • X-ray diffractometry analysis shows that the oxide consists of a phase of monoclinic WO 3 together with a sub-stoichiometric phase of the type WO 2 .83-
  • the anodization process according to the present invention generally allows modified tungsten oxide to be obtained in the form of a thin layer on the metallic surface of the tungsten electrode (usually a suitably sized lamina) subjected to anodization as described above.
  • the morphology and atomic composition of the tungsten oxide according to the present invention therefore refer to this surface layer, examined by means of electronic microscopy and XPS analysis, whose thickness can be qualitatively estimated within a range of 100 to 1,000 nm, according to the preparation conditions .
  • the surface of the WO 3 modified according to the present invention has a nanostructured morphology, i.e. it consists of elongated nanostructures of WO 3 having variable dimensions, but for over 95% included within lengths of 200 to 2,000 nm, having a morphology, as previously indicated, with an appearance similar to rice krispies.
  • the higher photoelectrochemical activity observed for the modified WO 3 photoanodes according to the present invention is thought to depend on this structural morphology, together with the doping action of the nitrogen atoms, with respect to the WO 3 photoanodes obtained by anodization processes currently known in the art, or by other known synthesis processes, for example, the chemical sol-gel preparation of nanocrystals from colloidal systems, according to what is described in international patent applications WO99/067181 and WO07/094019, and in the publications "C. Santato et al . J. Phys . Chem B 2001, 105, 936" and "C. Santato et al . J. Am. Chem. Soc . 2001, 123, 10639".
  • the photoelectrochemical activity observed for the modified WO 3 photoanodes, object of the present invention is higher than that of photoanodes obtained by anodic oxidation of metal tungsten laminas in electrolytic solutions based on ethylene glycol, water and NH 4 F.
  • the photoanodes are in fact capable of conducting currents having an intensity of up to about 5 mA/cm 2 in the presence of a bias equal to 1 V (with respect to a saturated calomel reference electrode - SCE) , under simulated solar irradiation (xenon lamp) at a power of 0,12 W/cm 2 .
  • This high photo-electrochemical activity is due to the capacity of the WO 3 photoanodes doped with nitrogen and having a morphology of the "Rice Krispies" type described above, of converting not only photons having a frequency falling within the spectral UV region into photocurrent, but also those having a frequency falling within the spectral visible region (up to 470 nm) .
  • the shift towards the visible region is strictly linked to the decrease in the band-gap (i.e. the difference in energy between the highest energy level of the valence band and the lowest energy level of the conduction band) of the WO 3 modified according to the present invention with respect to that of WO 3 prepared colloidally or also anodically in the absence of nitrogenated organic compounds.
  • WO 3 photoanodes prepared with electrolytic solutions comprising amides, in particular monoalkyl- substituted formamides, show high conversion percentages of photons to photocurrent (up to 65% of incident photons as can be seen, for example, from figure 5) .
  • Chrono-coulombometric analyses carried out on the modified WO 3 photoanodes according to the present invention also show a capacity of storing approximately double the electric charge with respect to that of WO 3 photoanodes obtained according to the known techniques of the state of the art, in particular with respect to those prepared by deposition of colloidal nanocrystalline films. From chrono-coulombometric data, in fact, it can be observed that in the photoanodes, object of the present invention, the active surface accessible to the solvent of the electrolytic solution and therefore exploitable for the production of photocurrents, is about double with respect to that of photoanodes based on the deposition of a colloidal nanocrystalline film.
  • the properties of the modified tungsten oxide, object of the present invention make the photoanodes produced with this oxide particularly suitable for applications based on photoanodic reactions.
  • a further object of the present invention therefore relates to a photoelectrolytic cell comprising a modified WO 3 photoanode according to the present invention.
  • Another object of the present invention also relates to a photoanodic process effected with the use of a modified WO 3 photoanode according to the present invention.
  • a further object of the present invention relates to a photo-production process of hydrogen from water ⁇ photo-splitting) carried out using a modified WO 3 photoanode according to the present invention.
  • the use of the WO 3 photoanodes described above is particularly advantageous, as the production of hydrogen is directly proportional to the photocurrent generated by the photoanode due to solar illumination.
  • a WO 3 photoanode was prepared starting from a lamina of metal W having a thickness of 0.5 mm and an area of 1 cm 2 by means of the potentiostatic anodic oxidation process, object of the present invention.
  • the anodization was carried out in an electrolytic solution having the following weight percentage composition:
  • the lamina was subjected to washing with deionized water and acetone and subsequently positioned in an ultrasound bath of distilled water for five minutes.
  • the lamina was then calcined in air at 550 0 C for 1 h.
  • a second modified WO 3 photoanode was prepared with the same equipment described in Example 1.
  • the anodization was carried out in an electrolytic solution having the following weight percentage composition:
  • a potential difference of 40 V was applied to the electrodes for 72 consecutive hours.
  • a third modified WO 3 photoanode was prepared with the same equipment described in Example 1.
  • the anodization was carried out in an electrolytic solution having the following weight percentage composition:
  • a potential difference of 40 V was applied to the electrodes for 72 consecutive hours.
  • a fourth modified WO 3 photoanode was prepared with the same equipment described in Example 1.
  • the anodization was carried out in an electrolytic solution having the following weight percentage composition:
  • ethylene glycol (EG) for the remaining weight percentage .
  • a potential difference of 40 V was applied to the electrodes for 72 consecutive hours.
  • a fifth WO 3 photoanode was prepared by deposition of a nanocrystalline film according to the process described in the work (Y. Guo et al . Environm. Sci. And Technol. 2007,41, 4422).
  • the anodization was carried out with the same equipment described in Example 1, containing an electrolytic solution having the following weight percentage composition:
  • the technique is based on the photoelectric effect, whereby the photo-electrons emitted from the surface of the irradiated sample are obtained and analyzed.
  • the sample is struck with a beam of low-energy electrons (neutralizer) .
  • the analysis area is circular with a diameter of about 0.4 mm and the depth of the sampling is 10 nm approximately. This is a surface analysis, capable of revealing the presence of surface closest chemical species.
  • a quantitative response is obtained from the XPS spectrum, relating to the atomic percentage of the most abundant elements, excluding hydrogen.
  • Single components of a particular chemical element with different electronic neighbourhood can also be obtained from the relevant spectra acquired in high resolution.
  • the peak corresponding to the orbital W 4f 7/2" served as internal energy reference, to define an absolute position on the scale of the abscissa, establishing its maximum being at 36.0 eV.
  • Other peaks, after energy correction, can be separated into their components, attributable to species with a different surrounding.
  • the XPS spectrum is expressed in terms of "Binding Energy" (B.E.), i.e. the energy necessary for removing a surface electron.
  • B.E. Binding Energy
  • the form of each peak provides further information (FWHM) and its area is proportional to the relative concentration of the chemical element in the analyzed layer.
  • XPS analysis showed that nitrogen atoms were inserted in the crystalline lattice of the WO 3 in varying concentrations with the electrolytic bath, as demonstrated by the broadening of the absorption band up to 470 nm. Nitrogen is in fact present in all the cases as contaminant, but it is more abundant on the surface of samples Fl and F3. Carbon atoms, on the other hand, are external contaminants positioned outside the lattice.
  • the photocurrent measurements can be effected either with two electrodes (photoanode 24 and cathode 25) , as represented in figure 2, or with three electrodes (photoanode - cathode - reference) .
  • a voltage generator (27) capable of providing the electrodes with the desired voltage with an increase rate of 10-20 mV/s, is connected externally between the anode and cathode.
  • the whole circuit is closed in the electrolytic solution 23 with the current of positive ions which migrate from the anode 24 to the cathode 25 in the opposite direction to the flow of electrons in the external circuit.
  • the cathode 25 consists of a commercial platinum screen with a high surface, connected to the voltage generator 27.
  • the photoanode 24, also connected to the generator 27 and ammeter 26, consists of a metal tungsten lamina having both surfaces composed of modified WO 3 obtained according to the previous examples 1 to 5.
  • the photoanode 24 is illuminated by a polychromatic xenon lamp 28 which simulates solar radiation (irradiation equal to 0.12 W/cm 2 ; filter AM 1.5).
  • the photocurrent produced by the photoanode 24 due to the incident radiation 29 is measured with an increase in the voltage applied to the electrodes (J-V curve) .
  • the voltage applied to the electrodes is measured with respect to a saturated calomel reference electrode (not shown in figure 2) .
  • the cell 21 is also provided with suitable devices for collecting the gaseous oxygen which is developed at the anode and the gaseous hydrogen which is developed at the cathode during the photoreaction.
  • Figure 3 shows the J-V curve relating to the electrodes obtained according to examples 1 (Fl) , 2 (F2), 3 (F3), 4 (F4) and 5 (F5) .
  • the curve indicates the attainment of currents of about 5 mA/cm 2 in correspondence with a bias equal to about 1.0 V towards SCE.
  • the intensity of the photocurrent is lower than 2.0 mA/cm 2 for bias values up to 1.5 V towards SCE (last section of the curve not shown in figure 1) .
  • the J-V curves of figure 3 therefore show the advantageous and unexpected effect of the use of electrolytic solutions containing nitrogenated organic solvents.
  • the conversion efficiency of the photons in photocurrent (IPCE) of samples F2 and F4 was determined by varying the wavelength of the incident radiation, by means of a monochromator, and measuring the maximum currents obtainable.
  • the IPCE value, or quantic efficiency value is obtained according to the following relation:
  • IPCE(A) K [J(A)/ A P] x 100
  • K constant depending on the measurement units
  • J(A) photocurrent density
  • A wavelength of the incident radiation
  • P power density of the incident radiation
  • a 100% IPCE corresponds to the generation of an electron for each incident photon.
  • Figure 4 shows the photo-action spectrum of sample F2 (NMF/HF (0,05%) /H 2 O (20%)).
  • the graph indicates the IPCE % values in relation to the wavelength of the incident radiation on the surface of the photoanode F2, at two different bias values (1.0 and 1.5 V) .
  • the sample F2 showed a maximum conversion value equal to 65% of the incident photons at a wavelength of about 350 nm .
  • the conversion of the photons in photocurrent for the photoanode F2 is significant up to wavelength values of about 470 nm (spectral visible region) .
  • sample F2 The performances of sample F2 are much higher than those of sample F4 (EG/NH 4 F (0,1%) /H2O (5%)) (comparative) , as can be observed from an analysis of the photo-action spectrum of figure 5.
  • sample F4 has a quantic efficiency generally lower than that of sample F2 for the whole width of the spectrum examined and, in addition, it does not produce significant quantic conversion efficiencies when the wavelength of the radiation is greater than 380 nm, whereas sample F2 maintains an IPCE higher than 15% in the portion of visible spectrum ranging from 380 to 430 nm.
  • the SEM analysis was carried out with a scanning electron microscope with a field emission (FE-SEM) model JEOL JSM 7600F.
  • Figures 6-7 show the photographs obtained with SEM for samples Fl and F5 respectively.
  • the photographs show the presence of a surface consisting of WO 3 particles having a morphology similar to that of Rice Krispies, with characteristic vermiform or branched swellings having an opening in central position extending longitudinally for the whole length of the swelling.

Abstract

La présente invention porte sur un oxyde de tungstène modifié ayant une concentration atomique de 0,5 à 7,0 %, de préférence de 2,0 à 5,0 %, d'atomes d'azote en position dans le réseau, par rapport au nombre total d'atomes de l'oxyde, ayant une morphologie de surface, détectable au moyen d'un microscope électronique à balayage, caractérisée par des nanostructures sous la forme de boursouflures ouvertes lombricoïdes ou ramifiées, de préférence ayant une longueur allant de 200 à 2000 nm et une largeur allant de 50 à 300 nm, ayant un aspect similaire au Rice Krispies. La présente invention porte également sur un procédé pour la préparation de l'oxyde ci-dessus par l'anodisation de tungstène métallique et également sur une photoanode comprenant l'oxyde ci-dessus.
PCT/EP2010/004404 2009-07-31 2010-07-08 Oxyde de tungstène modifié et son procédé de préparation WO2011012238A1 (fr)

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EP10732886A EP2459487A1 (fr) 2009-07-31 2010-07-08 Oxyde de tungstène modifié et son procédé de préparation
CN201080042159XA CN102548902A (zh) 2009-07-31 2010-07-08 改性氧化钨及其制备方法
US13/388,139 US20120186982A1 (en) 2009-07-31 2010-07-08 Modified tungsten oxide and process for its preparation

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ITMI2009A001394A IT1395728B1 (it) 2009-07-31 2009-07-31 Ossido di tungsteno modificato e processo per la sua preparazione
ITMI2009A001394 2009-07-31

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CN103252206A (zh) * 2013-05-19 2013-08-21 北京工业大学 一种花状氧化钨水合物吸附剂
CN107541746B (zh) * 2017-09-13 2019-06-11 西北师范大学 一种牺牲阳极钨片的液相阴极辉光放电等离子体制备纳米三氧化钨的方法
CN110004459B (zh) * 2019-04-28 2021-05-04 安徽大学 一种驱动二氧化碳还原的异质结光阳极及其制备方法和应用

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999067181A1 (fr) 1998-06-22 1999-12-29 Universite De Geneve Procede de fabrication d'une electrode comportant un film d'oxyde de tungstene
WO2007094019A1 (fr) 2006-02-17 2007-08-23 Nm Tech Ltd. Nanomaterials And Microdevices Technology Procede de fabrication de films nanocristallins transparents d'oxyde de tungstene

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7939218B2 (en) * 2004-12-09 2011-05-10 Nanosys, Inc. Nanowire structures comprising carbon
KR100894481B1 (ko) * 2007-04-16 2009-04-22 한국과학기술연구원 초극세 탄소 섬유에 축적한 금속산화물로 이루어진슈퍼커패시터용 전극 및 그 제조 방법

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999067181A1 (fr) 1998-06-22 1999-12-29 Universite De Geneve Procede de fabrication d'une electrode comportant un film d'oxyde de tungstene
WO2007094019A1 (fr) 2006-02-17 2007-08-23 Nm Tech Ltd. Nanomaterials And Microdevices Technology Procede de fabrication de films nanocristallins transparents d'oxyde de tungstene

Non-Patent Citations (7)

* Cited by examiner, † Cited by third party
Title
B. COLE ET AL.: "Evaluation of nitrogen doping of tungsten oxide for the photoelectrical water splitting", JOURNAL OF PHYSICAL CHEMISTRY, vol. 112, 3 July 2008 (2008-07-03), pages 5213 - 5220, XP002565408 *
C. SANTATO ET AL., J. AM. CHEM. SOC., vol. 123, 2001, pages 10639
C. SANTATO ET AL., J. PHYS. CHEM B, vol. 105, 2001, pages 936
D. PALUSELLI ET AL.: "Nitrogen doping of reactively sputtered tungsten oxide films", ELECTROCHEMICAL AND SOLID STATE LETTERS, vol. 8, no. 11, 2005, pages G301 - G303, XP002565409 *
K. NAKAGAWA ET AL.: "Electrochromism and electronic structures of nitrogen doped tungsten oxide thin films prpared by RF reactive sputtering", JAPANESE JOURNAL OF APPLIED PHYSICS, vol. 47, no. 9, 12 September 2008 (2008-09-12), pages 7230 - 7235, XP002565410 *
Y. GUO ET AL., ENVIRONM. SCI. AND TECHNOL., vol. 41, 2007, pages 4422
Y. GUO ET AL.: "High photocatalytic capability of self-assembled nanoporous WO3 with preferential orientation of (002) planes", ENVIRONMENTAL SCIENCE AND TECHNOLOGY, vol. 41, 5 September 2007 (2007-09-05), pages 4422 - 4427, XP002565411 *

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US20120186982A1 (en) 2012-07-26
CN102548902A (zh) 2012-07-04
EP2459487A1 (fr) 2012-06-06
IT1395728B1 (it) 2012-10-19

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